In the third generation partnership project (3GPP), there is a debate about installing, in the coverage of a large cell (macro cell), a number of small cells using a different frequency band (for example, a frequency band higher than that used in the macro cell). For example, as in the example of FIG. 1, a plurality of small cells that use a frequency band of 3.5 GHz are placed in the coverage area of a macro cell that uses a frequency band of 2 GHz.
In LTE Release 12, discussions have started concerning a technology called Dual Connectivity that makes two types of base stations cooperate under such an environment (NPL 1). The two types of base stations are a master eNodeB (a mater eNB, for example, the base station of a macro cell) and a secondary eNodeB (a secondary eNB, for example, the base station of a small cell). In the Dual Connectivity, the two types of base stations are connected via a wired or wireless backhaul channel. Note that a terminal apparatus can establish connection to both the master eNB and the secondary eNB and, for example, receive data from the two base station apparatuses.
In the Dual Connectivity, downlink signaling of a control signal to the terminal apparatus is done by the master eNB (NPL 1). On the other hand, in uplink, a control signal from the terminal is assumed to be transmitted not only to the master eNB but also to the secondary eNB. The master eNB and the secondary eNB can use a plurality of frequency bands each having a predetermined bandwidth. The terminal apparatus transmits the control signal in at least one of the plurality of frequency bands. Note that each of the plurality of frequency bands corresponds to, for example, the component carrier of a 20-MHz bandwidth. Note that each of the plurality of frequency bands that the master eNB and the secondary eNB can use is assigned, for example, a different unit for a baseband, and a different cell (communicable range) is formed in each of the plurality of frequency bands. That is, each of the master eNB and the secondary eNB is one base station apparatus but forms a plurality of cells in correspondence with a plurality of frequency bands. The set of the plurality of cells for the master eNB is called an MCG (Master Cell Group), and the set of the plurality of cells for the secondary eNB is called an SCG (Secondary Cell Group).